The present invention relates to a semiconductor laser element used for optical information processing, optical communication, etc.
It is known that the semiconductor laser performance can be enhanced by efficiently confining light in the active region. In the semiconductor laser elements of a multilayer structure, therefore, there have been employed the specific laminated structures such as double heterostructure (DH), separate confinement structure (SCH) and large optical cavity (LOC) for confining light in the direction vertical to the layers.
With the conventional crystal growing techniques such as LPE and MOCVD, however, it is difficult to selectively grow as a burying layer, a layer having a refractive index relatively small in comparison with the laminated layers for efficiently confining light in the direction parallel to the layers. Especially, in the case of AlgaAs-based semiconductor laser, although a semiconductor layer having a relatively small refractive index in comparison with an active layer could be formed as the burying layer, it was impossible to form as the burying layer, a semiconductor layer having a refractive index smaller than that of a cladding layer. It is therefore, for example, infeasible to confine light in the direction parallel to the laminations in the portion of the cladding layer, whereby there are disadvantages that a loss in the cavity is large and an internal quantum efficiency is low.
From studies by the present inventors on the subject matter, it has been found a technique for forming a burying layer in an LOC structure which is one of the lamination structures capable of efficiently confining light in the direction vertical to the layers and which comprises a first cladding layer, an optical guiding layer, an active layer and a second cladding layer formed on a substrate in this order or in reverse order, the burying layer being a semiconductor layer having a smaller refractive index than that of the cladding layer, and being disposed to side faces other than laser-emitting faces of the active layer and the optical guiding layer. The present invention was attained on the basis of this finding.